Mobile Assisted Handoff uses the fixed-duplexer spacing of paired forward and reverse communication channels, as is known for Code Division Multiple Access (CDMA) communication systems. A recent proposal (3GPP2 A.S0014-D v2.0 verification and validation version) uses a “Flex Duplex” capability where the paired forward and reverse CDMA communication channels are assigned in a non-fixed (i.e., flexible) duplexer spacing. With flexible duplexer spacing, any reverse CDMA channel from a band class can be coupled with any forward CDMA channel from that band class, or with a forward CDMA channel from another band class, subject to the capabilities of the mobile station (indicated by session attributes to the communication network). This also allows using a reverse CDMA channel from a paired spectrum with forward CDMA channels from both the paired spectrum as well as unpaired spectrum providing network operators with additional flexibility in spectrum allocation.
Unfortunately, CDMA-to-CDMA handoff time when using Flex Duplex is longer than necessary because the target base station is not informed of the forward and reverse channel assignment that is in use prior to the handoff. As a result, time is wasted sending target capabilities to the source base station that are not likely to be used during a handoff. In addition, time is wasted informing the source base station of a target base station's capability that, in some cases, has no chance for success. For example, the target base station could have determined, after receiving the handoff request message, that it does not support the handoff configuration of the currently in-use call and could have immediately rejected the handoff request. In addition, the CDMA-to-CDMA handoff success probability is lower than necessary.
Also, the time for the radio to synchronize may be reduced by assigning the currently in-use Flex Duplex Channel (FDC) for the handoff instead of picking a different set of channels for handoff. The time savings is due to avoiding the need to retune the radio channel and to avoiding the need to re-acquire synchronization. Also, by retaining the in-use Flex Duplex Channel during handoff, a known radio propagation condition is retained for the handoff procedure which would result in an improved handoff success rate.
One solution currently proposed in a cellular base station standard (to be published as 3GPP2 A.S0014-D v2.0) is for the target base station, during a handoff, to report its ability to support Flex Duplex. Specifically, Flex Duplex information is added to a Handoff Request Acknowledge message and to a Handoff Command message. The target base station, using the Handoff Request Acknowledge message, informs the source base station of the Flex Duplex capability of the target base station. The Flex Duplex capability is a list of forward and reverse channel pairs that the target base station supports. However, this solution does not address the Flex Duplex capabilities of the mobile station. In addition, this solution does not inform the target base station about the Flex Duplex capabilities presently in use for the communication to be handed off.